Add the rice, urad and chana dals and optional poha to a sieve and rinse with cool water (use your fingers to move and mix) for a minute, then discard the water. Transfer mixture to a large bowl (or 8 cup measuring bowl) and cover with water by 2 inches and soak for 4 hours. (See Note 2)
Working in batches, transfer half of the soaked and drained mixture to a Vitamix or high powered mixer and grind each batch with 1 cup water and 1 tsp sugar. Feel the batter, it should be completely smooth, no gritty chunks. It should look like a white pancake batter, but thinner in consistency. Free flowing, not clumpy and thick. Too thick and it will not ferment.
Transfer all the batter to the steel bowl of your Instant Pot. Top with glass lid, (not the IP seal lid), and push the Yogurt setting and change time to 12 hours.
Remove lid, you should see see air bubbles, it will smell slightly sour and the consistency will be a thick and foamy batter.
Add 2 tsp of kosher salt AFTER it ferments and mix thoroughly with hands or spatula for 1-2 minutes (this aids in fermentation). To check, you can drop some batter into a glass of water, it will float if it's fermented. If it sinks, cover batter again and ferment for another 2 hours.